Surface coated wax-polymer lubricant compositions

ABSTRACT

Lubricant compositions consisting essentially of free-flowing discrete particles of wax-polymer, the surface of which is coated with a wetting agent and a solid lubricant.

United States Patent 11113,607,746

[72] Inventor Gerard P. Caruso [56] Reference Cited A 1 N xg'g g UNITEDSTATES PATENTS fi 29 1968 Re. 26,088 9/1966 Rulon-Miller et al 252/12[45] Patented Se 1971 3,078,237 2/1963 Creech et al 252/59 [73] Assi neeoucom an 3,080,330 3/1963 Rudel et 31.... 252/59 g New York y 3,264,2158/1966 Smith etal.... 252/12 2 .'.1 V 3, 3,258,319 6/1966 Cox 252/593,438,896 4/1969 Council at al 252/12 541 SURFACE COATED WAX-POLYMERLUBRICANT "9" 'W- wyma" COMPOSITIONS Assistant Examiner-l. Vaughn 6Claims No Drawings Attorney-Harold L. Denkler [52] US. (I 252/12 [51]Int. Cl Cl0m 5/22, ClOm 5/ l2, ClOm 5/02 ABSTRACT: Lubricantcompositions consisting essentially of [50] Field of Search 252/12,free-flowing discrete particles of wax-polymer, the surface of 12.2,12.4, 12.6 which is coated with a wetting agent and a solid lubricant.

SURFACE COATED WAX-POLYMER LUBRICANT COMPOSITIONS This invention relatesto compositions to be used for lubricating railroad centerplates and forother heavy duty applications such as on caterpillar tractors,earth-moving equipment, etc., in which solid lubricants are necessaryfor satisfac tory performance. More specifically, this invention relatesto lubricating compositions consisting essentially of free-flowingdiscrete particles of wax-polymer, the surface of which is coated with awetting agent and a solid lubricant.

Changes in railroad car design and operating practices have demonstratedthe need for lubricants of greater serviceability than those used in thepast. With the addition of high-tonnage railroad cars into service, theproblems of wheel-flange wear, lateral thrust on general bearings,centerplate wear, etc., have become more and more acute. To overcomethese problems, there has been a general shift away from greases to theuse of solid lubricants such as molybdenum disulfide, graphite, powderedlead, etc., as centerplate lubricants. A satisfactory means of conveyingthe solid lubricant to the centerplate, however, has not been found.When solid lubricants are applied in a grease mixture, the force on thecenterplate quickly extrudes the grease carrying the solid lubricantwith it before the solid lubricant can bond to the metal surfaces.Mixtures of solid lubricants and wax have offered some improvement butthey still have a tendency to extrude, also the dispersion of the solidlubricant is not always homogeneous. The development of wax-polymersystems containing a homogeneous dispersion of solid lubricant, such asdescribed in application Ser. No.

746,772 Smith-Cokes filed July 23, 1968 and now abandoned, has resolvedsome of these problems. Other approaches included utilizing plasticliners which proved to be relatively successful in reducing extrusion,but were extremely expensive and therefore have limited practical use.Petroleum solvents were also employed as carriers for solid lubricants,but these are relatively volatile and do not provide secondarylubrication as does a system employing grease, wax, or waxpolymer.

It has now been found that the problems of the prior art can besubstantially overcome by employing lubricant compositions consistingessentially of discrete particles of waxpolymer coated with a wettingagent having a solid lubricant dissolved or dispersed therein.

The advantages of the compositions of this invention are immediatelyapparent. The wax-polymer particles, e.g., pellets, serve not only asthe carrier-vehicle but also impart a tough lubricating film whichadheres to the centerplate and allows sufficient time for the solidlubricant to bond to the metallic surfaces. It has an advantage over thehomogeneous waxpolymer solid lubricant system, in that the solidlubricant is readily available on the surface of the pellets and thusincreases the efficiency of use of the solid lubricant. The waxpolymerpellets are of sufficient consistency to resist extrusion from thecenterplate as is often experienced with grease or simple wax carriers.

The wax-polymer pellets used in accordance with this invention can beprepared from any conventional wax by adding thereto sufi'icient polymerto enable the resultant mixture to be pelletized. The preferred waxesfor this invention are petroleum waxes, either distillate or residualwaxes, or any combination thereof. Distillate waxes are defined as thosewaxes which are derived from the refining of distillate lubricatingoils, while the term residual waxes" refers to those waxes which areremoved during the refining of residual lubricating oils. The preferredpetroleum waxes generally have melting points of from about 120 to 180F. The distillate waxes are generally paraffinic in nature, while theresidual waxes may contain microcrystalline wax or high-melting pointparaffins or both. Residual waxes may, however, be further refined(split) to produce separate wax fractions which are essentiallymicrocrystalline or parafiinic in character.

The polymers used in the present invention can be characterizedgenerally as having long chain backbones to which randomly andirregularly are attached side chains of no more than about 4 carbonatoms in length. Particularly advantageous polymers are copolymers ofethylene with terminally ethyleniliiil Rt lti 1.

wherein n ranges from about 15 to about 250. The acetate substituentoccurs at random along the hydrocarbon chain, and thus the letter m"denotes the average number of ethylene units per vinyl acetate unit inthe molecule, rather than the presence of regularly recurring unitshaving the composition given within the brackets. The value of m rangesfrom 6.5 to 30, preferably from about 8 to 14.

The ethylene alpha-olefin copolymers which may also be used inaccordance with the invention have the general linear configurationwherein n is an average integer from about 10 to about 50 (preferably 10to 40), R is a hydrocarbyl radial having 1 to 4 carbon atoms and theunit (CH is an unbranched chain, the average molecular weight of thecopolymers being between about 20,000 to 800,000 (preferably betweenabout 200,000 and 400,000). Expressed as intrinsic viscosity (decilitersper gram), copolymers having intrinsic viscosities of between about 1.0and 6.0 are preferred. Intrinsic viscosity is determined in decalin at150 C. The mole ratio of ethylene to higher alkylene in the copolymercan be carried from about 60% to about 95%; however, more highlycrystalline copolymers, i.e., those having from about to ethylene arepreferred in order to avoid tackiness.

The aforementioned wax-polymer compositions are old and well known inthe art. Also known are methods of preparing pellets (sometimes referredto as nibs) from these waxpolymer blends. An often-employed methodinvolves pumping the molten wax-polymer blend through a die forming longstrings" which are cooled then cut into desired lengths. The size andshape of the pellets are not critical in the present invention. Pelletsmust of course be large enough to be free flowing and avoidagglomeration after the solid lubricant is applied, but not so large asto make them difficult to use in the desired application. Especiallysuitable pellets are cylindrical in shape, and are approximatelyone-eight inch in length by one-eighth inch in diameter. The pelletsgenerally comprise from about 5% to 30% of ethylene-vinyl acetatecopolymer blended with petroleum wax. The copolymer containsapproximately 25 to 28 mole percent of vinyl acetate.

Various types of solid lubricants are known to be useful in thelubrication of railroad centerplates. Solid lubricants which can becoated on wax-polymer pellets include but are not restricted to thefollowing: molybdenum disulfide, graphite, red lead, zinc oxide,copperflake, powdered lead, and powdered zinc. Many other solidlubricants can also be applied to the surface of wax-polymer pelletsemploying the method of the present invention. The amount of solidlubricant coated on the pellets can vary from about 5% to about 30% byweight.

The lubricating compositions of the present invention can be prepared bymoistening the wax-polymer pellets with a wetting agent, then stirringor mixing them in a vessel containing a predetermined amount of solidlubricants. An alternative method is to mix the wax-polymer pellets withthe solid lubricant then slowly add the wetting agent which wouldcomplete the adhesion of the solid lubricant to the surface of thewaxpolymer pellets. One other method of preparation is to blend thesolid lubricant and wetting agent together and then add the wax-polymerpellets and stir until the pellets are completely coated.

The wetting or adhesive agent can be any material capable of causing thesolid lubricant to adhere to the wax-polymer surface. Such materialsinclude but are not restricted to mineral lubricating oils, syntheticlubricating oils such as polymerized olefins, esters and others, andsynthetic fluids such as propylene oxide or silicon polymers. Minerallubricating oil is especially preferred and can be obtained from anyparaffinic, naphthenic, asphaltic, or mixed base crude. The viscosity ofthese oils may vary over a wide range, such as from about 50 to 6,500SUS at 100 F. Mineral oils having viscosities of about 57 to 3,000 SUSat 100 F. are preferred. The coating operation can be performed at roomtemperature or any other temperature which is convenient.

The amount of wetting agent used should be sufficient to provideadhesion of the desired amount of solid lubricant to the surface of thewax-polymer pellet, yet should not be so great as to cause sticking oragglomeration of the pellets and retard their free flow properties. Thepercentage of wetting agent can vary from about 1% to by weightdepending on its viscosity and the nature and amount of solid lubricantdesired to be coated. For example, when mineral oil is used as thewetting agent with a relatively large amount of solid lubricant, e.g.,of molybdenum disulfide as described in Example l, the amount of mineraloil which could be used ranged from 5.5% to 6.0% by weight. Compositionscontaining less than 5.5% by weight mineral oil resulted in the solidlubricant not completely adhering to the surface of the pellets, whichcompositions containing greater than 6% by weight resulted inagglomeration of the pellets.

The waxpolyrner pellets used in examples 1 to 7 were formed from a blendcomprising distillate and residual petroleum waxes blended withethylene-vinyl acetate copolymer. Typical composition of the pellets isas follows:

38.6% by volume, l40

refined wax) 12.8% by volume, 160 F.m.p., FRW

38.6% by volume l40 F.m.p. microcrystalline wax 10.0% ethylene-vinylacetate copolymer containing about 25 mole percent of vinylacetate(Elvax 360, commercially available from E. l. Dupont De NemoursCo.)

The following examples are illustrative of the invention:

F .m.p. (melting point), FRW (fully EXAMPLE l Wax-polymer pellets weremoistened with 500 l-lVl (High Viscosity Index, viscosity index of 85 orgreater) solvent neutral mineral oil then coated with 25% by weightmolybdenum sulfide by mixing the components in a vessel at roomtemperature. The resultant product was freeflowing coated wax-polymerpellets position:

25.0% by weight molybdenum disulfide 69.5% by weight wax-polymer pellets5.5% by weight 500 l-lVl neutral mineral oil having the followingapproximate com- EXAMPLE 2 5.5% by weight 500 l-lVl neutral mineral oilEXAMPLE 3 Wax-polymer pellets were moistened with 500 l-lVl neutralmineral oil then coated with 25% by weight red lead by mixing thecomponents in a vessel at room temperature. The resultant product wasfree-flowing coated wax-polymer pellets having the following approximatecomposition:

25.0% by weight red lead 69.5% by weight wax-polymer pellets 5.5% byweight 500 l-lVl neutral mineral oil EXAMPLE 4 Wax-polymer pellets weremoistened with 500 HVl neutral mineral oil then coated with 25% byweight zinc oxide by mixing the components in a vessel at roomtemperature. The resultant product was free-flowing coated wax-polymerpellets having the following approximate composition:

25.0% by weight zinc oxide 69.5% by weight wax-polymer pellets 5.5% byweight 500 l-lVl neutral mineral oil EXAMPLE 5 Wax-polymer pellets weremoistened with 500 V1 neutral mineral oil then coated with 25% by weightcopperflake by mixing in a vessel at room temperature. The resultantproduct was free-flowing coated wax-polymer pellets having the followingapproximate composition:

25.0% by weight copperflake 69.5% by weight wax-polymer pellets 5.5% byweight 500 l-lVl neutral mineral oil EXAMPLE 6 Wax-polymer pellets weremoistened with 500 HW neutral mineral then coated with 25% by weight ofpowdered lead by mixing the components in a vessel at room temperature.The resultant product was free-flowing coated wax-polymer pellets havingthe following composition:

25.0% by weight powdered lead 69.5% by weight wax-polymer pellets 5.5%by weight 500 l-lVl neutral mineral oil EXAMPLE 7 Wax-polymer pelletswere moistened with 500 HVl neutral mineral oil then coated with 25% byweight of powdered zinc by mixing the components in a vessel at roomtemperature. The resultant product was free-flowing coated wax-polymerpellets having the following composition:

25.0% by weight powdered zinc 69.5% by weight wax-polymer pellets 5 .5%by weight 500 HVl neutral mineral oil Further examples which areillustrative of the invention are:

EXAMPLE 8 Wax-polymer pellets are moistened with synthetic esterlubricant then are coated with 30% of molybdenum disulfide.

EXAMPLE E9 Wax-polymer pellets are moistened with a propylene oxidepolymer then are coated with 5% of copperflake.

EXAMPLE l0 Wax-polymer pellets are moistened with a silicone polymerthan are coated with 10% of powdered lead.

To demonstrate the effectiveness of the lubricating compositions of thisinvention, the coated pellets of Example 1 were applied to railway carcenterplates. This lubricant composition has now performedsatisfactorily for over 6 months.

1 claim as my invention:

1. A lubricant composition consisting essentially of freeflowingdiscrete particles of wax-polymer, the surface of which is coated with1% to by weight lubricating oil wetting agent and 5% to 15% by weightsolid lubricant, said wax-polymer comprising a blend of petroleum waxand 5% to 30% by weight of a copolymer of ethylene and a member selectedfrom the group consisting of the ester of a saturated mono-carboxylicacid and a terminally ethylenically unsaturated aliphatic alcohol, andthe ester of a saturated aliphatic alcohol and a terminallyethylenically unsaturated monocarboxylic acid and wherein said solidlubricant is a member selected from the group consisting of molybdenumdisulfide, graphite, red lead, zinc oxide, copperflake, powdered leadand powdered zinc.

2. The composition of claim 1 wherein the copolymer is a member selectedfrom the group consisting of ethylene-vinyl

2. The composition of claim 1 wherein the copolymer is a member selectedfrom the group consisting of ethylene-vinyl acetate, ethylene-propylene,and ethylene methyl methacrylate.
 3. The composition of claim 2 whereinthe copolymer is ethylene-vinyl acetate.
 4. The composition of claim 1wherein the wetting agent is selected from the group consisting ofmineral lubricating oil and synthetic lubricating oil.
 5. Thecomposition of claim 4 wherein the wetting agent is a minerallubricating oil having a viscosity of from 57 to 3,000 SUS at 100* F. 6.The composition of claim 5 wherein the solid lubricant is molybdenumdisulfide and the copolymer is ethylene-vinyl acetate.